In a modern parcel shipping installation, parcels proceed on a conveyor belt and an overhead dimensioning system determines the height, width and length of the individual parcels. Various dimensioning systems are based on different technologies. There are laser ranging systems, scanning systems, triangulated CCD camera/laser diode systems such as the DM-3000 Dimensioner (Accu-Sort), and LED emitter-receiver systems.
Downstream of the dimensioning system is typically a bar code decoder system. Again, various technologies are available including laser scanners and imagers and line scan cameras such as the SICK MVS series of cameras. Sometimes, the dimensioning system provides an output to the bar code decoder system to focus it on the parcel.
In order for the dimensioning system to be “legal for trade,” certain requirements must be met. Known dimensioning systems, hereinafter “general dimension” systems or subsystems, are primarily limited by their accuracy which is referred to as ‘d’. Regulations dictate that an object less than 12 d in any dimension cannot be considered legal for trade. See the National Conference on Weighing and Measures, handbook 44 and NTEP Publication 14. Other countries have similar requirements. Current state of the art general dimension systems offer 0.2 inches×d. This means that any object less than 2.4 inches in any dimension is not legal for trade. Thus, many current or general dimensioning systems are not sufficiently accurate to measure a parcel with one very small dimension, in one example, a box 14 inches long by 16 inches wide but only 2 inches high (e.g., a picture frame).